1. Field of the Invention
The present invention relates to methods for sensing when a person is about to fall asleep, and, more particularly, to methods for sensing when a vehicle operator is about to fall asleep.
2. Description of the Related Art
The U.S. National Highway Traffic Safety Administration estimates that approximately 100,000 police-reported crashes annually, about 1.5% of all crashes, involve drowsiness or fatigue as a principal factor. Drowsiness/fatigue may play a role in crashes attributed to other causes. About one million crashes annually (one-sixth of all crashes) are thought to be produced by driver inattention or lapses.
Systems for detecting driver sleepiness and alerting the drowsy driver have been developed. One such system works only if the driver's head falls forward and requires wearing a device on the driver's ear. In the case of the head falling sideways, the fluid-based mercury switch sensors of these known systems fail to trigger an alarm.
Another problem with these known driver sleepiness detection systems is that they trigger false alarms in the event that the driver intentionally tilts his head forward, such as if the driver looks at the floor in front of the driver's seat. That is, there is no second criterion used to verify the drowsiness of the driver.
Other known driver sleepiness detection systems determine a degree of driver drowsiness based upon a frequency and/or duration of the closure of the driver's eyelids. These systems sense eyelid closure based on a change in pixel color of given areas within a camera's field of view. A problem with such systems is that they may often erroneously decide that they have detected eye closure in response to changing lighting conditions within the passenger compartment of the vehicle or in response to the driver moving his head.
Accordingly, what is neither anticipated nor obvious in view of the prior art is a method of detecting driver drowsiness in response to the driver's head falling sideways. What is also neither anticipated nor obvious in view of the prior art is a method of detecting driver drowsiness based on both head movement and a second criterion that confirms the driver's drowsiness. What is further neither anticipated nor obvious in view of the prior art is a method of detecting driver drowsiness based on detected eye closure that is less likely to trigger false alarms in response to a change in passenger compartment lighting or to movement of the driver's head.